The present invention is directed to an apparatus for heat treating a heat treatable material such as metal feedstock or scrap by one or more individual or combined operations of preheating, decoating, and/or melting in an energy efficient and environment-friendly manner.
In recent years, recycling of process or post-consumer scrap materials has become increasingly critical in modern times for both environmental and economic reasons. The low-energy cost associated with recycling, combined with growing concerns over solid waste disposal, have contributed to substantial growth in the recycling industry. This trend has been observed in conjunction with many discarded products including beverage cans, metal turnings from manufacturing plants, recyclable household garbage, aluminum foil, discarded glass and bottles, foil packaging materials, steel products, and the like.
Known recycling processes generally involve melting reusable components of waste or scrap material and recasting the same into useful products through the use of gas- or oil-fired reverbatory furnaces or induction electric furnaces. However, these and other similar methods and apparatuses for recycling scrap materials typically require substantial capital expenditure and maintenance expense, generate substantial harmful atmospheric emissions, and require significant energy input. The development of an energy-efficient, environmentally-suitable apparatus for treating metal scrap and other materials is desired to ensure that the recycling industry complies with the energy and environmental performance requirements set forth by tighter regulatory legislation while improving overall profitability of recycling.
The treatment of such materials so that they may be suitable for recycling is problematic because the materials often have coatings of various materials, especially organic materials including protective coatings, lubricants, additives and the like. Successful recycling processes typically mandate that the coatings be removed before the underlying material is recycled. This process often requires separate installations.
A recent apparatus, referred to as a vertical flotation melter (xe2x80x9cVFMxe2x80x9d), was developed in response to environmental and economic needs and to provide a cleaner and more efficient alternative for melting scrap material. During the melting operation, scrap material is introduced into an upper opening of an upstanding melting chamber where scrap materials of varying sizes, shapes, densities, and surface areas are maintained in a state of suspension by a continuous stream of hot gas flowing upwardly from the lower portion of the chamber. During the suspension phase, heat is transferred from the upwardly flowing gas to the scrap material being treated. When the temperature of the scrap material exceeds its melting point, the solid scrap melts and forms into denser, aerodynamically shaped liquid droplets which fall downwardly through the upwardly directed heated gas. The resulting drops of molten material are collected for subsequent recovery and use.
Such known VFMs suffer from several significant limitations. In particular, the heated gas is directed into the heating chamber through a single port. The upward flow of the gas from a single port is non-uniform which severely restricts a) the overall output rate of recovery, b) the types of material which may be recovered, and the overall thermal and energy efficiency of the heat treating operations. In addition, the lower portion of the melting chamber of known VFMs tend to become blocked from the buildup of the melted scrap material. Such blockages severely degrade the overall operating efficiency and performance of the VFM and may require time consuming shutdowns which add significantly to the cost of operation.
It would therefore be a significant advance in the art of heat treating heat treatable materials and/or the recovery of reusable materials to provide an improved heat treating apparatus with increased recovery yields and reduced emissions in a cost effective and efficient manner. Furthermore, the apparatus may be adapted for use with a range of raw and scrap materials and may be used for various heat treating operations alone or in combination, including preheating, decoating, melting and combinations thereof.
The present invention is generally directed to a heat treating apparatus for treatment and/or recovery of useful materials such as metals, glass and the like from a variety of sources. The heat treatable materials include those containing vaporizable impurities typically in the form of coatings. The heat treating apparatus is operated and implemented in a manner which provides benefits of improved energy efficiency, product yield, and operating cost. The apparatus is adaptable for use as a preheater, a decoater, a melter and any combination thereof.
In one particular aspect of the present invention, there is provided an apparatus for heat treating a heat treatable material, comprising:
a) a housing comprising an upper opening for receiving a heat treatable material at a first temperature, a lower opening, and a chamber therebetween for heating the heat treatable material to a second temperature higher than the first temperature as the material moves through the chamber from the upper opening to the lower opening;
b) a gas supply assembly operatively engaged to the housing at the lower opening, and comprising a source of heated gas, a gas delivery assembly for delivering the gas through a plurality of pathways into the housing in a manner providing countercurrent flow to movement of the heat treatable material, whereby the heat treatable material passes through the lower opening at said second temperature as a heat treated material; and
c) control means for controlling conditions within the chamber to enable the heat treatable material to reach the second temperature and form said heat treated material and pass through the lower opening at the second temperature.
Another aspect of the present invention is directed to a method for heat treating a heat treatable material, comprising the steps of:
a) passing the heat treatable material through a housing from an upper opening at a first temperature through a chamber and out of a lower opening;
b) passing a heated gas through a plurality of pathways into the chamber to generate a flow of the heated gas countercurrent to the direction of the heat treatable material as it passes from the upper opening to the lower opening in a manner such that the heat treatable material leaves the lower opening as a heat-treated material at a second temperature higher than the first temperature; and
c) controlling the conditions within the chamber to enable the heat treatable material to attain the second temperature.